Canon lens focuses on P not on 7

[Goody]

I have an odd Canon issue. I have a 7 and a P -- both focus correctly with a Canon 50mm 1.8 and a Nikkor 50mm f2. I recently got a Canon 100mm f3.5. It works perfectly on the P but on the 7 the focus is quite off when focussed with the rangefinder; both on film and by the distance scale (comparing the distance scale with a tape measure). On the 7 the RF will not converge at infinity when the lens is set there -- but focus is correct when set by scale focus. Any thoughts?

 

[Peter Jennings]

Set the shutter at T and open the back. Fire the shutter and look inside while focusing. Check to make sure the focus cam of the lens is lined up properly with the roller on the RF arm. Sounds like they aren’t lining up correctly.

 

[Goody]

Thanks - I will try that with the 100mm on both bodies and with one of the 50's that does work on both bodies.

 

[Peter Jennings]

On 50mm lenses, the surface that rides against the RF arm roller goes all the way around the circumference of the base of the lens. That is why this only happens with the 100mm lens. On the 100, there's only about a centimeter of the lens that can contact the roller.

 

[Goody]

Set the shutter at T and open the back. Fire the shutter and look inside while focusing. Check to make sure the focus cam of the lens is lined up properly with the roller on the RF arm. Sounds like they aren’t lining up correctly.

You are exactly right - on the P the cam sits slightly off center to the raised portion of the 100mm lens that roller contacts, but well within the "flat zone"; on the 7 it's right at the very edge, I think overlapping into the angled part, so it's not registering exactly on the flat. As you said on the 50's there is no raised portion so the "horizonal" position of the roller is not important.

Now my question is whether the 7 can be adjusted or is it the lens that needs adjustment? The P was CLAed but the 7 hasn't been.

 

[Peter Jennings]

I'm pretty good at diagnosing, but fixing the issue is something I have no idea of. I would assume it's not a fixable issue, but I could be wrong. Is your 100mm an early version from the 50s or an all black version from the 60s?

 

[Goody]

I wrote to Don Goldberg and he said the roller on the camera (rangefinder arm) isn't, to his knowedge, adjustable and he didn't hold out a lot of hope on the lens. Basically if the raised portion of the lens that engages the roller was rotated to a little more vertical it would solve the problem. Attached is a photo showing the mismatch of the roller to the flat -- the roller on the 7 just misses being completely on the flat. Oddly the roller on the P is a little more centered in the retangular cutout and does engage the lens correctly.

 

[Dante_Stella]

On cheaper lenses, you can take nail polish and a file to adjust the cam engagement angle. Kind of a nuclear solution, but that's how the factory did it.

 

[Peter Jennings]

I just mounted my early version 100mm on a Canon 7s to compare to your picture above. My lens rotates a few millimeters further than yours - just enough for the cam and roller to properly engage. You could try Dante's idea. If I understand it correctly, you'd build up lacquer on the end of the cam and file it down flush with the surface of the brass? I did something similar with epoxy on a dropped lens with a bent cam to raise the surface. Epoxy would be a more durable solution.

 

[Phil_F_NM]

Can you clean the flange sides on camera and lens then make sure the lens is screwed on perfectly flush? I've used as well as repaired a bunch of lenses like this one and have never seen this problem before.
There could be a way to move the intermediate cam arm in the lens. I seem to recall one of my old lenses that used this system had some adjustment provision.
Phil Forrest

 

[Goody]

Flange on camera and back of lens seem totally clean. The weird thing is it focusses fine on my Canon P -- the lens doesn't seem to screw in farther -- it's just that the roller is more centered on the camera. Anyway at least it works on the P -- just wish it would work on the 7 which has a longer base RF.

 

[retinax]

It's probably not worth it but if the cam cannot be moved, rotating the lens mount on the camera would be another possibility. How well do other lenses screw on? Do they end up with the infinity mark more or less on top?
To your consolation, the 100 mm frame lines in the 7 are awfully small. And the accuracy of the RF isn't that great on mine, it reads different distances at the right and the left sides of the RF patch. Is that better on the P?

 

[Goody]

I am not sure how accurate the RF on the 7 is but I've not had any trouble with it, of course with 50mm lenses. The 100mm frame is bigger in the P (1:1 vs .8 viewfinder) but the RF baseline is a lot smaller, so I believe it's overall less accurate -- but maybe accurate enough. In terms of rotating the lensmount there are 4 screws so even if it created no issues (not sure if the screws are evenly spaced) it would be too much rotation to help. I'm thinking I have a lens a little out of spec and a Canon 7 on the edge of spec in the opposite direction.

 

[iphoenix]

In terms of rotating the lensmount there are 4 screws so even if it created no issues (not sure if the screws are evenly spaced) it would be too much rotation to help. I'm thinking I have a lens a little out of spec and a Canon 7 on the edge of spec in the opposite direction.

Hi,

My experience with this type of problem:

I had a VT serviced and afterwards, lens didn't have the correct infinity position and the focus was out. After returning it twice without it being fixed, I tried turning the body's lens mount around 90 degrees. It fixed both problems.

On my latest arrival (an L2), though all my Canon and most of my LSM lenses focussed correctly, my Elmar 90/4 didn't. After tightening the lens mount screws, It does now (as the others do still).

Check where the lens's focus cam is at infinity and then (guess/estimate/observe) where the body's focus rotor is at the same time.

At least this is worth checking.

Good Luck,

David

 

[Goody]

The amount it's off isn't much - a few degrees. On the 100mm there is a raised portion on the back of the lens, of about 1/2 or 3/4 inch in length for the roller to engage - on the P it hits fine on the 7 it's slightly off the edge. The screws in the lens mount are snug. I do think my 7 is slightly out of spec as the roller in off center in it's little cutout, but as I mentioned DAG doesn't think that is fixable.

 

[davhill]

The amount it's off isn't much - a few degrees. On the 100mm there is a raised portion on the back of the lens, of about 1/2 or 3/4 inch in length for the roller to engage - on the P it hits fine on the 7 it's slightly off the edge. The screws in the lens mount are snug. I do think my 7 is slightly out of spec as the roller is off center in it's little cutout, but as I mentioned DAG doesn't think that is fixable.

Is the lens also out of spec, or is the issue completely in the 7? If you know someone nearby who also has a Canon 100, it'd be worth trying theirs on your 7 body to see if the issue remains. If the lens itself is out, methinks you have only two alternatives: Build up the roller flange on the lens with industrial epoxy to give it a longer flat, or use it only on the P. Or (3) sell the lens [cheap] to some unsuspecting soul who only has a P.

P.S. I only have a P, and sorely lack a 100. Just sort of noting that. Nothing implied. 🙂

 

[Goody]

I'm thinking of sending the 7 to Don Goldberg for a CLA -- perhaps he will see something causing the roller to be off center. It probably needs a CLA anyway after all these years....

 

[Goody]

P.S. I only have a P, and sorely lack a 100. Just sort of noting that. Nothing implied. 🙂

That's funny!!

 

[Mackinaw]

I'm thinking of sending the 7 to Don Goldberg for a CLA -- perhaps he will see something causing the roller to be off center. It probably needs a CLA anyway after all these years....

Years back, I had an old Canon 85/1.9 LTM lens that had a terrible wobble. The internal barrel was loose. It had the same type of focusing cam as your 100mm, the type with the “tongue.” I tried to fix the lens myself by taking it apart. I did managed to take it apart but never fixed it. But I did notice that the barrel that houses the focusing cam could be moved. So the position of the cam can be adjusted. At least it could on the 85/1.9.

Jim B.

 

[iphoenix]

That's funny!!

Does somebody have a CB radio?😉